This is the 400th most frequent Icelandic word.
góðum
The Icelandic word "góðum" is the dative plural form of "góður," meaning "good" in English.
Here, "góðum" is an adjective in the dative case, plural, describing "bókum."
Ég mæli með góðum bókum fyrir þig.
I recommend good books for you.
The word "góðum" is used as an adjective in the dative case, plural form, describing "skilningi".
Ég tala við nemanda í góðum skilningi.
I talk to the student with good understanding.
In this sentence, "góðum" functions as an adjective in the dative case, plural, describing "vinum."